Siruri de caractere - trasformari & isalnum

#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;

int main()
{
    char ch,s[100]={};
  int n;
  cin.getline(s,100);
  n = strlen(s); ///lungimea sirului
  for(int i=0;i<n;i++){
   // if((s[i]>='a' && s[i]<='z')||(s[i]>='A' && s[i]<='Z')) //isalnum
    if(s[i]>='A' && s[i]<='Z'){
      s[i]=s[i]+('a'-'A'); ///transformare 'G'--> 'g'
    }
    else
    if(s[i]>='a' && s[i]<='z'){
      s[i]=s[i]-('a'-'A'); ///transformare 'G'--> 'g'
    }
      cout<<s[i]<<" ";
  }

}